Undrained Monotonic Shear Response of MICP-Treated Silty Sands

Abstract

The effect of nonplastic fines on the undrained shear response of sand depends on many variables, including fines content, skeleton void ratio (es), interfine void ratio (ef), global void ratio (e), confining pressure, and relative density. This paper focuses on applying microbe-induced carbonate precipitation (MICP) to silty sands containing fines up to 35% to assess its effect on the undrained shear response. Sporocarcina pasteurii, an alkalophilic soil bacterium was used to catalyze the chemical reaction and induce calcium carbonate precipitation. Shear-wave velocity (Vs) measurements are used to assess improvement, with a target Vs of approximately 4 m/s. Undrained monotonic direct simple shear loading was used to compare the undrained shear response of untreated and MICP-treated specimens with similar preshear void ratios of .7±.5. Decreased excess pore water pressure and flow behavior and increased undrained shear strength were the observed general changes due to MICP. The results presented here indicate that the effect of MICP on silty sands depends on relative density, fines content, and the fabric governing the structure of the soil.